Apparatus for continuously molding sheet material

ABSTRACT

Apparatus is disclosed for producing molded sheet material. An endless belt-type mold is entrained over rolls, providing an upper run and a catenary. Molten thermoplastic material is extruded onto the upper run and caused to assume the configuration of the belt mold by the action of vacuum applied from beneath the belt before the molten material solidifies. The molded sheet material is stripped from the belt mold near the end of the upper run, and apparatus is provided fro efficiently cooling the catenary of the belt mold before molten material is applied again.

United States Patent Davis et a1.

[54] APPARATUS FOR CONTINUOUSLY MOLDING SHEET MATERIAL [72] lnventors:Leonard P. Davis; Robert M. FJliott,

both of Kingsport, Tenn.

[73] Assignee: Kimberly-Clark Corporation [22] Filed: May 27,1970

[21] Appl. No.: 40,952

511 1111.01 ..B29 17/04 58 Field of Search ..1s/4 B, 4 c, 5 A, 15 s, 15R, 18/15 F, 15 v, 19 F; 264/47, 90, 91, 210,

[56] References Cited UNITED STATES PATENTS 1,157,149 10/1915 Conger..l8/15S 14 1 Aug. 22, 1972 3,099,043 7/1963 Held ..l8/l9 F X PrimaryExaminer-J. Spencer Overholser Assistant Examiner-Lucius R. FryeAttorney-Cecil D. Quillen, Jr. and John F. Stevens [57] ABSTRACTApparatus is disclosed for producing molded sheet material. An endlessbelt-type mold is entrained over rolls, providing an upper run and acatenary. Molten thermoplastic material is extruded onto the upper runand caused to assume the configuration of the belt mold by the action ofvacuum applied from beneath thevbelt before the molten materialsolidifies. The molded sheet material is stripped from the belt moldnear the end of the upper run, and apparatus is provided fro efficientlycooling the catenary of the belt mold before molten material is appliedagain.

5 Claims, 4 Drawing Figures llffimimuszwn 3.685.930

SHEET 1 0F 2 LEONARD R DAVIS ROBERT M. ELLIOTT ATTORNEY b'INVNT I 4%mmrtmum 1972 My H I 1 u I II 1 I J; n

v 0 I6 fjlj h I O LEONARD I? DAVIS RRRRRRRRRRRRR TT TTTTTT EY Thisinvention relates to the continuous molding of thermoplastic material,and more specifically, this invention relates to apparatus for moldingcontinuous sheets of thermoplastic material into variousthreedimensional configurations from a falling curtain o moltenmaterial.

Conventional methods and apparatus for producing three-dimensionalproducts from sheet material include those in which the sheet materialis embossed usually after the application of sufficient heat to softenthe material, so that it can easily be thermoformed. The presentinvention provides a novel apparatus for producing a continuous sheet ofmolded material by extruding a falling curtain of the thermoplasticmaterial directly onto an endless belt-type mold traveling below a filmdie. In this manner, the necessity of first making the flat sheet iseliminated.

According to this invention, apparatus is provided for supporting aflexible, endless belt-type mold for travel along a predetermined path.A driving roll is supported at one position on a suitable frame and anidler roll spaced therefrom. The belt is entrained over the two rollsthereby providing upper and lower runs. A

' curtain-type extruder or film die is positioned above the upper run ata position remote from the end of the upper run. Means are provided fordrawing a vacuum under and through the belt mold at a position slightlydownstream from the extruder. Material formed in the belt mold isstripped therefrom near the end of the upper run. Also, according to thepresent invention, means are provided for cooling the belt mold betweenthe point where the material is stripped off and the point where thefalling curtain of extruded material contacts the belt mold. Significantadvantages are obtained by cooling the belt mold at this position.Increased production rates are achieved by the apparatus according tothis invention. Conventional heat removal methods such as passing thebelt mold over chill rolls cannot be used effectively because of thehigh thermal resistance of the belt mold material, which is usually avery flexible silicone rubber. Free connection heat transfer severelylimits production rates, or requires the use of extremely long belts.Forced convection cooling with air or gas blowing parallel to the beltis little better than free convection because much of the mold surfaceis not exposed to the air stream due to the configuration of the mold.The otherwise sheltered surfaces can be reached and relatively largeheat transfer coefficients obtained by using two-dimensional air jetsdirected generally perpendicular to the belt mold.

It is an object of this invention to provide apparatus for continuouslymanufacturing molded sheet material directly from an extruded fallingcurtain of molten thermoplastic material.

It is a further object of this invention to provide novel means foradequately cooling the belt mold between the point where the moldedsheet material is stripped ofi and the point where the falling curtaincontacts the mold, thereby considerably shortening the required lengthof the belt mold.

These and other objects of the invention will become apparent from thefollowing disclosure with reference to the drawings.

In the drawings which illustrate a specific embodiment of the invention:

- FIG. 1 is a side elevation view showing a continuous molding machineaccording to our invention;

FIG. 2 is a section view taken substantially along line 2-2 of FIG. 1;

FIG. 3 is an enlarged elevation view of the cooling apparatus accordingto our invention; and

FIG. 4 is an enlarged plan view of the cooling apparatus.

Referring to FIGS. 1 and 2, frame 10 has rotatably mounted thereoncylinders 12 and 14 over which a continuous belt-type mold 16 isentrained, having an upper run 18 and catenary or lower run 20. Thebelttype mold 16 is of a durable, flexible material such as, forexample, silicone rubber. To prevent stretching and consequentdistortion of the mold 16, it is usually desirable to attach a backingbelt 22, which may be of fabric or similar material. The mold 16 andbacking belt 22 are connected, such as by adhesive connection orstitching. Means are provided for finely adjusting the distance betweenrolls 12 and 14 which include the screw-type adjuster 24. Horizontalmovement of roll 12 can be achieved by turning the screw 26 which isconnected to the bearings 28 and 30 of roll 12.

An extruder head 32 is provided above the upper run 18 of the belt mold16 for extruding a molten curtain 34 of thermoplastic material onto thesurface of the belt mold 16 near the beginning of upper run 18. Moltenthermoplastic material, for example, polyethylene having a melttemperature of 350425F., is supplied to the extruder head 32 from supplymeans (not shown). The curtain 34 falls by gravity to the surface of themold 16, and is immediately molded to the configuration of the belt moldby means of vacuum being applied from beneath the belt mold 16 and thebacking fabric 22. The belt mold, although of a non-porous material suchas silicone rubber, is perforated at selected intervals for thetransmittal of vacuum through it. Generally, the perforations are at thebase of each of the depressions in the belt mold. Vacuum is applied tothe underside of the belt mold 16 and backing fabric 22 through suctionbox 36 over which the upper run travels. Suction box 36 is connected toa source of vacuum (not shown) through conduit 38.

Means are provided for extruding the curtain 34 directly into catchbasin 40 for start-up, etc., when it is not desired to extrude thecurtain onto the belt mold 16. Frame 10, which carries the belt mold l6,and frame 42, which carries the extruder head 32, and catch basin 40 aremovable relative to each other. This relative movability mayconveniently be established by means of rollers 44 which support theframe 10. Thus, for start-up, frame 10 may be moved to the right, asshown in FIG. 1, allowing extrusion into the catch basin 40. Materialextruded into the catch basin 40 can then be recirculated throughconduits 46 and 48, back to the extruder head 32 by means of the pump50.

As the curtain 34 is extruded onto the belt mold 16, movement of thebelt in the direction of the arrow is accomplished by means offrictional engagement of the backing fabric 22 with driving roll 14.Roll 14 is driven by means of motor 52 through belt 54 at apredetermined speed, depending upon the characteristics of curtain 34and the desired thickness of the molded sheet 56. As the belt 14carrying the-extruded curtain 34 thereon passes over vacuum box 36, themolded sheet material 56 is vacuum formed and solidified as it continuesto move along the upper run. As the material 56 reaches the end of upperrun 18 and enters the are over roll 14, it is stripped from the mold.Stripping the material at this position is greatly facilitated by thedepressions in the mold stretching and opening slightly when passingthrough this arc. The molded sheet material 56 is then passed over idlerrolls (not shown) and wound in a roll (not shown).

As the belt mold 16 is subjectedto intense heat in other material whileit is on'the upper run of the belt mold and before it is completelysolidified, the present invention is a marked improvement overconventional apparatus. The forced convection cooling apparatus pennitshigher production speeds with shorter belts, thus resulting in a savingsin cost as the mold belts are expensive to fabricate. The coolingapparatus according to this invention permits the entire surface area ofthe mold to be efficiently cooled even with the highly irregularconfiguration of the belt mold, in which some of the surfaces may beapproximately perpendicular to the plane of the belt. These difficultiesare overcome by the use of impinging two-dimensional air jets directedperpendicular to the belt mold 16 in a specific manner.

The relative position of the belt mold 16 and the cooling air chamber 70is shown in FIGS. 1 and 2. In FIG. 3, however, an enlarged view of thecooling air chamber 70 is presented. The cooling air chamber 70 isprovided with a nozzle plate 72 generally matching the contour of thecatenary of lower run 20. The nozzle plate 72 is spaced from the beltmold 16 a generally constant distance, D. Cooling air is supplied froman air conditioning unit 74 through duct 76 into the chamber In FIG. 4,a plan view of the cooling air chamber 70 is shown having a plurality ofjets 80 extending substantially across the width of the chamber 70. Thejets 80 are of uniform width and extend in a generally perpendiculardirection to the direction of travel of belt mold 16. The jets areactually in the form of slots provided in the nozzle plate 72 of chamber70. Cooling air is discharged through the nozzles 80 against the beltmold 16. Large heat transfer coefiicients are achieved with relatively'small quantities of air. The jets may be oriented so as to direct thecooling air up to 90 from the perpendicular to the plane of the belt,with the preferred orientation being substantially perpendicular to thebelt mold 16. The nozzles 80 may be oriented 90 from the direction oftravel of the belt mold 16, with the preferred orientation beingsubstantially perpendicular to the direction of belt travel.

As stated hereinbefore, for eflicient cooling of the belt mold 16, thejets 80 should be spaced a distance D from the lower run of the beltmold. This distance may be approximately three-eighths inch toapproximately 1% inches. The preferred distance is approximatelyseven-eighths inch.

Although air has been referred to herein repeatedly as the coolingmedium, it is contemplated that other gasses may be used with equallygood results.

Cooling can be accomplished to any desired degree depending on theoperating conditions of the apparatus. For example, the followingconditions represent a typical operation:

Length of belt mold-approximately 15 feet Width of belt mold-32 inchesDiameter of rolls l2 and 148.3 inches Extrusion ratelb./hr.

Width of extruder nozzle32 inches Speed of belt-55 ft./min.

Length of cooling air chamber-48 inches Number of nozzles23 Size ofnozzles-26 X 54; inches Capacity of refrigeration unit-3 tons, 1,200 CFMTemperature of molten thermoplastic material- The invention has beendescribed in detail with particular reference to preferred embodimentsthereof, but it will be understood that variations and modifications canbe effected within the spirit and scope of the invention.

We claim:

1. Apparatus for continuously molding sheet material comprising, incombination a. an endless, flexible belt mold having an irregularmolding surface integrally formed therein and a plurality of openings indepressed areas thereof,

b. means for supporting and advancing said belt mold in a positiondefining an upper run and a catenary,

c..a film die adapted to extrude a molten curtain of thermoplasticmaterial onto the upper run of said belt mold,

d. means for applying a vacuum to the underside of the belt tocommunicate with the openings in said belt at a position downstream fromsaid extruder,

e. means for withdrawing molded sheet material from the end of the upperrun, and

f. means for cooling said belt mold over at least a portion of itscatenary including an air distribution chamber having an upper sideformed of a nozzle plate, a series of generally transverse slits formedin said nozzle plate for directing air in a direction generallyperpendicular to said belt mold, said nozzle plate conforming generallyto the catenary of the lower run of said belt.

2. Apparatus according to claim 1 in which said irregular moldingsurface includes portions extending generally perpendicular to the planeof the belt mold.

3. Apparatus according to claim 1 in which said air distribution chamberextends over a major portion of the length of the catenary of said beltmold and the nozzles extend substantially the width of the belt mold.

4. Apparatus according to claim 1 in which each of the nozzles islocated between three-eighths inch and 1% inches from the catenary ofsaid belt.

5. Apparatus according to claim 1 which includes a catch basinpositioned below the lower run of said belt mold and under saidextruder, and said extruder and catch basin being movable relative tosaid belt mold whereby molten thermoplastic material may be extrudeddirectly into said catch basin.

1. Apparatus for continuously molding sheet material comprising, incombination a. an endless, flexible belt mold having an irregularmolding surface integrally formed therein and a plurality of openings indepressed areas thereof, b. means for supporting and advancing said beltmold in a position defining an upper run and a catenary, c. a film dieadapted to extrude a molten curtain of thermoplastic material onto theupper run of said belt mold, d. means for applying a vacuum to theunderside of the belt to communicate with the openings in said belt at aposition downstream from said extruder, e. means for withdrawing moldedsheet material from the end of the upper run, and f. means for coolingsaid belt mold over at least a portion of its catenary including an airdistribution chamber having an upper side formed of a nozzle plate, aseries of generally transverse slits formed in said nozzle plate fordirecting air in a direction generally perpendicular to said belt mold,said nozzle plate conforming generally to the catenary of the lower runof said belt.
 2. Apparatus according to claim 1 in which said irregularmolding surface includes portions extending generally perpendicular tothe plane of the belt mold.
 3. Apparatus according to claim 1 in whichsaid air distribution chamber extends over a major portion of the lengthof the catenary of said belt mold and the nozzles extend substantiallythe width of the belt mold.
 4. Apparatus according to claim 1 in whicheach of the nozzles is located between three-eighths inch and 1 1/2inches from the catenary of said belt.
 5. Apparatus according to claim 1which includes a catch basin positioned below the lower run of said beltmold and under said extruder, and said extruder and catch basin beingmovable relative to said belt mold whereby molten thermoplastic materialmay be extruded directly into said catch basin.